Fixed a bug with the utf8 word "Array" in a buffer causing a crash.

Putting the word "Array" in a utf8 buffer causes the program to crash.

```javascript
var buffers = concat(function(err, out) {
  console.log('buffers', err, out.toString())
})
buffers.write(new Buffer('pizza Array is not a ', 'utf8'))
buffers.write(new Buffer('stringy cat'))
buffers.end()
```

This is a possible security vulnerability for servers using this library to process requests.